This present invention relates to a method and apparatus for automatically moving a microfiche card including a large number of frame images in matrix so as to position a required frame in an optical projection path, projecting the required frame image onto a screen.
There is provided, in a microfiche card, a matrix arrangement of a large number of frames arranged in X (column) and Y (row) directions and within each frame there is photographically recorded an image containing information of high density, so that microfiches are widely used on various fields wherein an extremely large quantity of information must be dealt with. In order to project a required or selected frame image on the microfiche card onto a screen, a microfiche projection apparatus is used. The microfiche projection apparatus comprises an optical system for projecting a required or selected frame image onto a screen, a stage movable along a path in X and Y directions on which the microfiche card is placed and held, two pulse motors for moving the stage along a path in X and Y direction, respectively, a memory means which stores frame data corresponding to code numbers of respective frames on the microfiche card, and a micro-computer for individually controlling the pulse motors based on the frame data retrieved from the memory means upon the entry of the code number of a required frame to be projected. Upon specifying a required frame by its code number, the micro-computer retrieves the frame data which represent the location numbers in X and Y direction, the location number meaning where the required frame is from the reference or datum frame in each direction. Using the symbols PF(X) and PF(Y) for location numbers of the frame in X and Y directions, respectively, and the symbol N for the number of pulse signals required to shift the microfiche card by one frame in either X or Y direction by means of pulse motors, the address numbers NS(X) and NS(Y) which represent the numbers of pulse signals required to move the microfiche card in X and Y directions from the datum position wherein the datum frame is in the optical projection path to a position wherein a required frame is in the optical projection path are given by the following equations; EQU NS(X)=PF(X).times.N (1) EQU NS(Y)=PF(X).times.N (2).
Assuming the address numbers of the frame now in the optical projection path are represented by the symbols OS(X) and OS(Y), the signal number MS(X) and MS(Y) which represent the numbers of pulse signals required to shift the microfiche card directly from the present position to the required position wherein the required frame is in the optical projection path are given by the following equations; EQU MS(X)=NS(X)-OS(X) (3) EQU MS(Y)=NS(Y)-OS(Y) (4)
wherein it should be understood that the rotational direction of pulse motor depends on whether the result from the equation (3), or (4) is negative or positive. Consequently, direction and duration of the rotation of the pulse motor are controlled by the arithmetically derived result from the equation by the micro-computer so as to locate the microfiche card in a required position, positioning a required frame image in the optical projection path.
In conventional microfiche projection apparatus described above, the address number of a required frame is obtained from the product of the location number frame and the predetermined number of pulse signals by which a rotation of pulse motor is controlled to cause a motion of the microfiche card by one frame. In this X-Y positioning, it would be very desirable that the number of pulse signals for the motion of microfiche card by one frame be an integer. A predetermined number of pulse signals having a fraction is unfavorable in accurately locating the microfiche card in a proper position because of accumulated error. Assuming, for example, the rotational motion of the pulse motor per one pulse causes a microfiche card to move 0.5 mm and the length of the side of a frame in both X and Y directions is "9.8" mm, the number of pulse signals required to move a microfiche card by one frame, which is actually "19.6," becomes "20" by counting fractions of "0.5" and over as a unit and omitting the rest. There thus occurs a positional error corresponding to "0.4" pulse signal for every frame, resulting in the microfiche card getting out of position where a required frame is to be positioned every time the microfiche card is moved. Consequently, the frame image gets out of proper position on a screen.